Our previous studies have shown that murine tumor cells sensitive to natural killer (NK) or natural cytotoxic (NC) cellmediated lysis have to capacity to specifically bind laminin in a time and concentration dependent manner while tumor cells resistant to NK/NC killing bind much less laminin. Furthermore, we have shown that NK cells express a structure on their surface which is immunochemically cross reactive with laminin. These finding suggest that laminin and laminin receptors may provide a mechanism by which natural cellmediated cytotoxic cells recognize potential targets. The observation that the addition of exogenous laminin to NK or NC killing assays inhibits tumor cell lysis by preventing NK/NC target binding supports this hypothesis. The overall goal of this research proposal is to precisely define the role of laminin and laminin receptors in murine NK and NC killing of tumor cells. Two specific aims will be carried out. The first will focus on the NK and NC effector cells. We will use flow cytometry to compare the binding of affinity purified and monoclonal antilaminin antibodies with the binding of antibodies to known NK markers by populations of murine spleen cells. Both single color and two color fluorescence will be done. (We will also use antilaminin antibodies in the presence or absence of complement in an attempt to modulate NK and NC binding to target cells and NKand NCmediated killing of these cells). Finally, we will use immunochemical and biochemic approaches to purify and characterize the laminin-like antigens on the NK/NC cell surface. In the second specific aim we will focus on the potential target cells. We will characterized the laminin binding capacity and sensitivity to NK- or NC-mediated killing of several murine tumor cell lines. We will attempt to isolate from these populations, cells lines with liminin-binding capacity relative to that of the parent populations. The variant lines will then be determine whether laminin/laminin receptors on NK susceptible tumor cells contribute to their sensitivity to lysis by NK cell derived cytolytic factors (NKCF) and whether such cytolytic factors are immunochemically crossreactive with laminin. We hope that these studies will provide definitive evidence for the role of laminin and laminin receptors in the recognition and killing of murine tumor cells by natural cell mediated effector cells.